Cellular organic rigid thermosetting plastic foams used for thermal insulation are well known in the art. Foams can be made with urethane linkages, or made with a combination of both isocyanurate linkages and urethane linkages, or they can be made via the well known condensation reactions of formaldehyde with phenol, urea, and melamine. All such plastic foams must utilize an expansion agent, often referred to as a "blowing agent".
The prior art is replete with references to techniques of expanding foam cells. For many years, the dominant blowing agent for all thermosetting foams was trichloromonofluoromethane (CFC-11). Other types of blowing agents have been proposed, such as the use of hydrocarbon mixtures, taught in U.S. Pat. No. 3,558,531. In recent years, various foam expansion methods have been taught in such U.S. Pat. Nos. as the following (all of which are incorporated herein by reference): 3,993,609, 4,636,529, 4,898,893, 4,927,863, 4,981,876, 4,981,880, 4,986,930, 4,996,242, 5,032,623, 5,070,113, 5,096,933, 5,114,986, 5,130,345, 5,166,182 5,182,309, 5,205,956, 5,213,707, 5,227,088, 5,234,967, 5,236,611, 5,248,433, 5,262,077, 5,277,834, 5,278,196, 5,283,003, 5,290,823, 5,296,516, 5,304,320, 5,314,926, 5,318,996, and 5,336,696.
The relatively recent hydrogenated chlorofluorocarbons (called "HCFCs") are considered to be environmentally friendly expansion agents, but still contain some chlorine, and therefore have an "Ozone Depletion Potential" (called "ODP"). Because of the ODP, the HCFCs have been mandated for eventual phaseout.
Another known class of blowing agents is the non-chlorinated, partially hydrogenated fluorocarbons (called "HFCs") which have the general formula: H.sub.z F.sub.y C.sub.z, where x, y, and z are integers. The HFC compounds being proposed for future blowing agents have two serious defects: (1) high intrinsic thermal conductivity properties (i.e., poor thermal insulation); and, (2) expense. In view of the fact that approximately ten percent by weight of rigid foam insulation are the compounds used as blowing agents, high cost combined with the poor insulating value render HFCs less attractive candidates for blowing agents in commercial foam insulation.
Hydrocarbon blowing agents are also known, which class includes halogen-free and CO.sub.2 -free blowing agents. For example, U.S. Pat. No. 5,182,309 to Hutzen teaches the use of iso- and normal-pentane in various emulsion mixtures. Another example of hydrocarbon blowing agents is taught by Volkert in U.S. Pat. No. 5,096,933, pointing out the virtues of commercial cyclopentane distilled and extracted from natural gas wells.
However, the hydrocarbon blowing agents mentioned in connection with such prior art have inadequate miscibility with polyester polyols, commonly used in polyisocyanurate modified polyurethane foam. The use of these alkanes require a chemical surfactant to obtain a suitable mixture. An improvement in the problem of poor miscibility is taught in U.S. Pat. No. 5,166,182 to Blanpied, whereby the use of azeotropes with polar organic solvents enhance the miscibility with polar polyester polyols. However, all of that work was done using cyclopentane extracted from natural gas.
Another problem with some of these alkanes is the poor insulating value. For example, the thermal conductivity of n-butane at 25.degree. C. is 16.3 mW/m*.degree.K., and n-pentane at 25.degree. C. is 14.8 mW/m*.degree.K.
None of the prior art patents known to Applicants discuss how the cyclopentane is obtained for the disclosed foaming process, nor is there any recognition that any certain mode of cyclopentane production may endow the cyclopentane with properties which are beneficial for a foaming operation.
Although some cyclopentane originates from petroleum, most cyclopentane originates from natural gas wells, and is extracted as the bottom layer of distillation in a refinery, allowing the lighter molecules to be transferred through the natural gas pipeline network. Cyclopentane obtained by extraction contains impurities. In fact, cyclopentane sold as "Technical Grade" contains from 22% to 30% impurities.
One route for manufacturing cyclopentane involves recovery by distillation from naphtha streams derived from crude oil or field natural gasoline. Very limited quantities of cyclopentane can be produced via this route due to the low concentrations of naturally occurring cyclopentane. Furthermore, cyclopentane product purity via this route is limited to approximately 75% by the presence of 2,2-dimethyl butane (which has a boiling point less than 1.degree. F. (0.55.degree. C.) different from cyclopentane). Further purification requires more expensive processing such as extractive distillation.
Extracted cyclopentane ("EXTRCP") has at least five problems which heretofore virtually prohibited it from being considered a serious candidate as a commercial blowing agent for rigid foam insulation. The first problem is that its limited supply is considerably below the amount needed is to meet the quantity demanded of a commercial compound. The second problem is that this inadequate supply contains at least twenty-two percent impurities in the form of hexane isomers and n-pentane, which impurities significantly reduce insulating value of foam made therefrom. The third problem is that extracted cyclopentane is not miscible with the common polyester polyols which are used with HCFCs nor those that were used with CFC-11.
The fourth problem is that extracted cyclopentane does not reduce the viscosity of the polyester polyol foamable blend to a workable level, even when liquid fire retardants are utilized.
The fifth problem is that the foam produced with EXTRCP will not pass the ASTM E-84 maximum 75 Flame Spread Index even with moderate flame retardant.
With respect to the third and fourth above-mentioned problems, the above-discussed U.S. Pat. No. 5,096,933 to Volkert, while generally alluding to the use of polyester polyols, provides no specific example using polyester polyols. The lack of any specific example is consistent with the present inventors' understanding that mixtures made from polyester polyols and extracted cyclopentane are unstable mixtures. In this regard, extracted cyclopentane is no more suitable as a miscible blowing agent than n-pentane or iso-pentane. All three require chemical surfactants for miscibility.
Perhaps the largest obstacle to the use of hydrocarbon blowing agents in the United States is the fifth problem--flammability of thermoset plastics blown with hydrocarbon blowing agents. U.S. Pat. No. 5,096,933 to Volkert mentions disadvantages caused by the flammability of the cycloalkanes. Volkert alludes to the optional use of flame retardants, but provides no example utilizing a flame retardant. Furthermore, none of the five Polyurethane Rigid Foam examples shown by Volkert would pass the maximum Flame Spread Index (FSI) of 75 (ASTM E-84) required of construction foam in the United States. Likewise, a polyisocyanurate foam, with out flame retardant, having an Isocyanate-to-Polyester Polyol INDEX of 2.3 badly failed the ASTM E-84 maximum Flame Spread Index requirement of 75, by achieving a 2174 FSI.
With regard to flammability, it is well known that organic surfactants contribute to the flammability of rigid plastic foam insulation. The three main classes of organic surfactants (anionic, cationic, and nonionic) all add to the flammability problem of plastic foam. However, the use of organic carbonates, such as ethylene carbonate and propylene carbonate, does not increase the flammability of plastic foam.
TABLE I describes experiments attesting to the immiscibility of extracted cyclopentane with the polyester polyol having the most miscible potential with non-polar hydrocarbons, as well as the immiscibility of n-pentane and iso-pentane with this polyester polyol. The first column of TABLE I shows the weight ratio of polyester polyol to hydrocarbon blowing agent, with the proposed blowing agents n-pentane, iso-pentane, and extracted cyclopentane being shown in the second through fourth columns, respectively. In all experiments, the polyester polyol utilized was Stepanpol PS-2502A, which (along with Cape's 245-C) is known to have the best miscibility with non-polar hydrocarbon blowing agents. In the experiments reflected by the first row of TABLE I, pure (no other chemicals) PS-2502A polyol was used at 80% weight with 20% by weight pentane; and so forth as indicated in the first column of TABLE I. Significantly, all experiments showed the polyester polyol to be immiscible with extracted cyclopentane, just as it is with n-pentane and iso-pentane.
TABLE I ______________________________________ IMMISCIBILITY STUDIES Weight Ratio (Polyol/Blow- Extracted ing Agent) N-Pentane Iso-Pentane Cyclopentane ______________________________________ 80/20 Separates Separates Separates 75/25 Separates Separates Separates 70/30 Separates Separates Separates 50/50 Separates Separates Separates 35/65 Separates Separates Separates 20/80 Separates Separates Separates ______________________________________
The fourth problem of extracted cyclopentane (EXTRCP) is shown in TABLE II below, where viscosity is high when blended in foamable blends.
TABLE II __________________________________________________________________________ CHEMICALS: Pbw Pbw Pbw Pbw Pbw Pbw Pbw Pbw Pbw Pbw __________________________________________________________________________ PS-2502A 100 100 100 100 100 100 100 100 100 100 Fyrol PCF -- -- -- -- -- 15 15 15 15 15 Dabco K-15 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 PM-DETA 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 DC-5357 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2.0 Water -- -- -- -- -- 1.8 1.8 1.8 1.8 1.8 Prop Carb -- 5.0 10 -- -- -- 5.0 10 -- -- Tex NP-9 -- -- -- 5.0 10 -- -- -- 5.0 10 EXTRCP 20. 20. 20. 20. 20. 23. 23. 23. 23. 23. Brookfield 6928 4016 2392 4480 2880 2725 * * 1810 1124 Viscosity __________________________________________________________________________ * denotes that an unstable emulsion separated (broke) rapidly. Viscosity cps at 65.degree. F.
TABLE II shows that, without exception, every blend made with extracted cyclopentane produced a Brookfield viscosity over 1000 cps at 65.degree. F., even one with 10 parts by weight of a strong viscosity reducer, Texacols NP-95. The foamable blends using both Fyrol PCF and Propylene Carbonate mixed into an unstable emulsion which soon separated. The inability to formulate with both liquid flame retardant and an organic carbonate is a serious obstacle to obtaining both flame resistance and a low enough viscosity to be workable.
In addition to obtaining cyclopentane by extraction, it appears that cyclopentane can also-be synthesized from other hydrocarbons. In this regard, FR-A-2595092 and FR-A-2595093 teach the preparation of catalysts comprised of palladium with another transition metal such as ruthenium or rhodium for the cyclization and hydrogenation of 1,3-pentadiene, as well as the hydrogenation of cyclopentadiene, to cyclopentane. These French Demandes do not teach or suggest the synthesis of cyclopentane from dicyclopentadiene ("DCP"), or make any reference to foaming processes.
GB-A-2271575 and GB-A-2273107 disclose two similar methods for synthesizing cyclopentane from dicyclopentadiene. GB-A-1302481 teaches a method which synthesizes minor amounts of cyclopentane, but preferentially produces cyclopentene. While GB-A-2271575 and GB-A-2273107 mention initially the search for blowing agents for polyurethane foam, neither provides an example of the use of cyclopentane as a blowing agent for foam, much less a foam produced with polyester polyol. In fact, European practice is to make polyurethane foam using polyether polyol rather than polyisocyanurate foam using polyester polyol.
Historically, considerable attention has been directed to the synthesis of cyclopentadiene and various isomers of the pentadiene and pentene building-block monomers. In this regard, dicyclopentadiene ("DCP"), C.sub.10 H.sub.12, is the dimer of cyclopentadiene ("CP"), C.sub.5 H.sub.6, and is the naturally stable form of CP. Cyclopentadiene monomer spontaneously dimerizes at room temperature. DCP is obtained from the thermal cracking of high molecular weight hydrocarbons, such as naphtha and gas oils, particularly in the presence of steam.
Owing to its conjugated double bonds, CP can undergo numerous reactions, and has several important commercial uses. While most commercial CP is obtained from cracking DCP, CP is also obtained from other commercial reactions such as ethylene production. To prevent it from autodimerizing, CP must be cooled to below minus 20.degree. C. To prevent spontaneous oxidation, CP must be protected from atmospheric oxygen. Thus, it is advantageous to convert DCP into cyclopentane in an enclosed reactor utilizing an excess of hydrogen, and adding cyclopentane as a diluent, as shown in GB-A-2271575 and GB-A-2273107.
The thermocatalytic conversion of DCP to CP, and back again, and similar processes, have been well documented. However, such conversion and similar processes have not occurred in the context of utilization for a blowing agent for a rigid insulative foam which utilizes polyester polyol.
The similar processes mentioned above include use by Alder and Stein of palladium as a catalyst to polymerize and hydrogenate DCP into the trimer form, then to tetracyclopentadiene, and finally into pentacyclopentadiene. Hydrogenation and polymerization to tetrahydrotricyclopentadiene has also been accomplished with Adams' platinum catalyst at room temperature and fifty pounds per square inch pressure. Bai, Zhang, and Sachtler of the Center for Catalysis and Surface Science, Northwestern University, reported using palladium adducts in 1991 for cyclization and hydrogenolysis reactions of neopentane and other hydrocarbons. U.S. Pat. No. 4,178,455 to Hirai et al. teaches that a transition metal catalyst, with a Lewis acid promoter, will convert urea biurets, and allophanates into corresponding urethanes.
Another possible route for manufacturing cyclopentane involves hydrogenation of cyclopentene; however, cyclopentene is not readily available in commercial quantities.
Another route to produce a high purity cyclopentane, and the subject of the present invention, involves splitting dicyclopentadiene (DCPD) into cyclopentadiene (CPD) monomer and hydrogenating the monomer to form cyclopentane. A key advantage of this route is an abundance of commercially available, low-cost DCPD raw material. Technical obstacles involve: (1) effective splitting of DCPD without forming heavy resins that diminish product yields and foul the splitting equipment; and (2) preventing unwanted reaction of the highly reactive monomer which decreases desired product yield, form unwanted by-products, and can lead to deactivation of the hydrotreating catalyst.
Thus, it is an object of the present invention to provide a thermosetting foam utilizing the advantages of specially synthesized cyclopentane ("SYNCP") as an improved insulating gas inside closed cells.
Another advantage of the present invention is the utilization of a hydrocarbon blowing agent which is readily miscible with common polyester polyols without requiring organic surfactants to make a stable blend.
An advantage of the present invention is the ability to create a foamable blend viscosity low enough to use in existing pumps without the requirement for additional viscosity reducing diluents.
Yet another advantage of the present invention is the utilization of an abundant source of specially synthetically produced cyclopentane, which insures that the costs will be contained in a reasonable range.
Still another advantage of the present invention is the achievement of a thermosetting foam having an ASTM E-84 Flame Spread Index less than the maximum 75 allowed.